1. Field of the Invention
The present invention relates to a mobile communication system enabling a mobile telephone being connected with the system to continue to connect the system when the mobile radio telephone is moved in an area where there is no ground stations by roaming or hand-over via a satellite communication.
2. Description of the Prior Art
FIG. 1 is a system configuration diagram showing a conventional mobile communication system. In this figure, reference numeral 1 denotes a public network, reference numeral 2 denotes a private system A which is a mobile communication system connected to the network 1. Reference numeral 3 denotes a private branch exchange hereinafter referred to as PBX, which employs, for example, an electronic exchange device. Reference numerals 4a, 4b, 4e and 4f denote a radio base station which is under control of PBX 3 and covers a respective communication zone. Reference numerals 5, 6a and 6b denote a mobile telephone carried by a user, which is connected to one of the radio base stations 4a, 4b, 4e and 4f by radio wave. In this application, the word "mobile" is so defined as to include the word "portable".
Reference numeral 10 denotes a private system B which is a mobile communication system, being connected to the public network 1. Reference numeral 11 denotes a PBX for the private system B. Reference numerals 12h and 12i denote a radio base station which is under control of the PBX 11 and covers a respective communication zone. Reference numeral 13 denotes a mobile telephone carried by a user and is connected to one of the radio base stations 12h, 12i by radio wave.
FIG. 2 is a system configuration diagram showing another conventional mobile communication network. In the figure, the same reference numerals are attached to the same elements as those in FIG. 1 and duplicate explanations are omitted.
Reference numerals 8h and 8i denote a public radio base station which is connected to the public network 1 and covers a respective communication zone. Reference numeral 9 denotes a mobile telephone carried by a user, which is to be connected to one of the public radio base stations 8h and 8i.
FIG. 3 is a functional block diagram showing a construction of the mobile telephone 5. In this figure, reference numeral 41 denotes a private protocol processing section which processes a private protocol of the private system, reference numeral 42 denotes a private control channel controlling section which controls private control channel for sending the private protocol. Reference numeral 43 denotes a public protocol processing section which processes a public protocol for accessing the public network 1. Reference numeral 44 denotes a public control channel controlling section which controls a public control channel for public protocol transmission. Reference numeral 45 denotes a transmitting/receiving section which is switched over by the switch 47 and is connected either to the private control channel controlling section or to the public control channel controlling section 44.
FIG. 4 is a functional block diagram showing a structure of a mobile telephone used in another mobile communication system. In the figure, the same reference numerals are attached to the same elements as those in FIG. 3 and duplicate explanations are omitted.
As shown in the FIG. 4, switches 46a and 46b are added to the mobile telephone illustrated in FIG. 3. The switch 46b is provided in order to connect the private protocol processing section 41 with the private control channel controlling section 42 and in order to connect the public protocol processing section 43 with the private control channel controlling section 42 via the switch 46a. The switch 46a is also used for connecting public protocol processing section 43 with public control channel controlling section 44.
FIG. 5 is a functional block diagram showing a structure of the radio base stations 4a-4f of the private system A illustrated in FIG. 2. These radio base stations are used in a mobile communication system where a PBX is installed which has a function to pass the information relevant to a mobile telephone which does not belong to the system A to the public network 1. In FIG. 5, reference numeral 51 denotes a transmitting/receiving section which is to be connected to the transmitting/receiving section 45 of the mobile telephone 6 by radio wave. Reference numeral 52 denotes a private protocol processing section which controls the private control channel. Reference numeral 53 denotes a private protocol processing section which processes a private protocol. Reference numeral 54 denotes a public protocol processing section which processes a public protocol. Reference numeral 55 denotes a line processing section which connects the radio base station to the PBX 3.
FIG. 6 is a functional block diagram showing a structure of the PBX 3. In FIG. 6, reference numeral 61 denotes a line interface to which the radio base stations are connected. Reference numeral 62 denotes a system discriminating function section which determines whether a received call is issued from a mobile telephone 5 belonging to the own system or it is issued from a mobile telephone 6 not belonging to the other private system. Reference numeral 63 denotes a private protocol controlling section which controls a call when the result of determination by the system discriminating function section is the own system. Reference numeral 64 denotes a different system protocol controlling section which connects a call to the public system when the result of the determination by the system discriminating function section 62 is different system. Reference numeral 65 is a network interface which connects the private protocol controlling section 63 and the different system controlling section 64 to the public network 1.
In FIG. 2, a connection request for the subscriber's telephone 25 of the public network 1 from the mobile telephone 9 is processed at the public protocol processing section 43 and an access to the public network 1 is made from transmitting/receiving section 45 under the control of the public control channel controlling section 44. In this case, therefore, identification and accounting are performed at the public protocol processing section 43 of the mobile telephone 9.
On the other hand, a connection request for the own system from the mobile telephone 5, 6a, or 6b is processed at each private protocol processing section 41 as shown in FIG. 3 and sent to the private control channel controlling section 42. Under the control of the private control channel controlling section 42, the request is sent from the transmitting/receiving section 45 to the radio base station 4 whose communication zone the mobile telephone 5 exits in.
At the radio base station 4, the transmitting/receiving section 51 receives the request and sends it to the private protocol processing section 53 via the private control channel controlling section 52 and the request is processed there and sent to the PBX 3 via the line processing section 55.
A connection request to the public network 1 via the private system A from the mobile telephones 6a, or 6b of FIG. 1, which does not belongs to the private system A, is processed at the public protocol processing section 43 of each mobile telephone, which is shown in FIG. 4, and is sent to the private control channel controlling section 42. Under the control of the public protocol processing section 43, the request is sent from the transmitting/receiving section 45 to the radio base station 4.
At the radio base station 4, the transmitting/receiving section 51 of FIG. 5 receives the request and sends it to the public protocol processing section 54 via the private control channel controlling section 52 and the request is processed there and sent to the PBX 3 via the line processing section 55.
The PBX 3 has a function to access calls from the own system only on private control channels. A connection request from the radio base station 4 is received at the line interface 61 of FIG. 6 and is sent to the system discriminating function section 62.
FIG. 7 shows the system identifier 222 of the control information 22 included in the connection request.
FIG. 8 is a flowchart showing the operation of the system discriminating function section. The system discriminating function section 62 compares the system identifier 222 at step S801 and judges whether the connection request is sent from the mobile telephone 5 which belongs to the own system or from the mobile telephone of the other private system at step S802. When the request is sent from the mobile telephone which does not belong to the own system at step S804, a procedure that the mobile telephone 6 carries out the authentication and accounting of the connection to the public system for this connection request is made at step S805 by the different system protocol controlling section 64.
On the other hand, as a result of the discrimination of the system discrimination function section 62, when the request is sent from the mobile telephone 5 which belongs to the own system, the PBX 3 performs the connection if the connection request is a connection request within the system. Further, if the connection is a public connection request, the request is sent from the own system protocol controlling section 63 to the public network 1 via the network interface 65. When the request is sent to the public network 1, the PBX 3 itself performs authentication and accounting processes.
Documents in relation to the above described conventional art of the mobile communication system include "Second Generation Wireless Telephone System, 1st ed. Standard RCR STD-28" published by Research and Development Center for Radio systems and Japanese Patent Application Laid-Open No. 2-192329.
Since the conventional mobile communication system is constructed as explained above, there is a problem that when the mobile telephone 5 connected to the radio base station 4 in the private system 2 moves out of the communication zone of the private system 2 while making a communication and the mobile telephone 5 is out of the coverage of the communication zone of the other system, a line connection to and from the mobile telephone 5 cannot be made.